1. Field of the Invention
The present invention relates to an electron emission source that is expected to be applied to flat type solid display elements, and more particularly relates to a cold cathode type electron emission element that realizes the integration and low voltage operability and a process for forming the cold cathode type electron emission element.
2. Description of Prior Art
Heretofore, the hot cathode type electron emission element has been used popularly, however, electron emission by use of a hot electrode is disadvantageous because of large energy loss due to heating and because of requirement of pre-heating.
On the other hand, a small cold cathode structure has been realized with progress of vacuum micro-electronics technology, and the cold cathode type electron emission element has attracted attentions recently. Among the cold cathode type electron emission element, field effect type electron emission element, in which a high voltage is generated locally for field emission, has been developed actively.
FIG. 1 is a schematic partial cross sectional view showing an example of a conventional field effect type electron emission element. In FIG. 1, 11 denotes a substrate consisting of silicon (Si), 12 denotes an insulating layer consisting of SiO2 formed on the substrate 11, 13 denotes a gate consisting of metal layer, and 14 denotes a circular cone electrode consisting of molybdenum (Mo).
In the case of the electron emission element having the structure as described hereinabove, when a voltage is applied between the substrate 11 and the gate 13, electrons are emitted from the cusp of the electrode 14 where a strong electric field is applied.
Furthermore, to realize a high performance electron source that is operable with a lower driving voltage than that of the conventional electron source, the reduction of the gate aperture and fabrication of a cathode having a steeper tip have been tried by applying LSI technology.
Though the conventional electron emission element is operable with a low voltage because it has a cone-shaped cathode having a small diameter and steeper tip as described hereinabove, this type of electron emission element is disadvantageous as described herein under.
At first, material having a low electron emission threshold value (electron affinity is small) is suitably used as electron emissive material, and metal W, metal Mo, nitride and oxide of these metals have been tried to be used. However, pure material that can be formed in the shape of cone configuration is limited as long as the conventional fabrication technique is employed.
Furthermore, electron emission stability and evenness are included in the most important performance to be considered when an electron source is to be used practically. In the conventional example, the emission current of a cathode is influenced strongly by the vacuum environment in operation and surface state of a top end of the cathode, and the physical property of the surface, for example, the work function of a current emission part, is changed during current emission to results in significant change of the operation current. As the result, the above-mentioned required performance is not satisfied. The reason is likely that emitted electrons collide with residual gas drifting near the cathode to generate ions, and the ions collide against the top end of the cathode to change the surface state of the top end of the cathode.
A process in which a cathode comprises a plurality of multi electron sources arranged at the time and the individual electron emission fluctuation is leveled to stabilize the emission current has been proposed to suppress the current fluctuation, however, the fluctuation has been still problematic in practical application because the fabrication process of cone-shaping is complex and the cone shape scatters significantly.
Furthermore, use of such field emission type electron source as CRT electron source has been tried, however, the fine electron beam, which is preferable for high vision system to obtain high definition, results in poor brightness. In other words, the tradeoff relation between brightness and definition is problematic.
The present invention has been accomplished in view of the above-mentioned problem, and the object of the present invention is to form fine structure on a cathode surface evenly and reproducibly with simple working process and to increase and stabilize the emission current value.
To solve the above-mentioned problem, in a cold cathode forming process of the present invention, a target material and a substrate are provided in a reaction chamber, the pressure (P) of an ambient gas introduced into the reaction chamber and the distance (D) between the substrate and the target material are controlled so that the size of a high temperature high pressure area formed near the target material by irradiating a beam light onto the target material is optimal, and the material contained in the target material is excited and ejected by irradiating the beam light onto the target material with introducing the ambient gas into the reaction chamber at the pressure to deposit the material on the substrate. The above-mentioned structure is effective not only for simplification of the manufacturing process and cost reduction but also for obtaining self align type crystalline structure.
An electron emission part of an electron emission element of the present invention comprises a cold cathode having a crystalline thin film of electron emissive material formed by means of the above-mentioned cold cathode forming process. The above-mentioned structure is effective for realizing the reduced electron emission threshold value and the increased emission current value and stability, and realizing the reduced cost with the structure simpler than the conventional structure.
Furthermore, the present invention provides a cold cathode forming process characteristically comprising a step for providing a target material and a substrate in a reaction chamber, a step for controlling the pressure (P) of an ambient gas introduced into the reaction chamber and the distance (D) between the substrate and the target material so that the size of a high temperature high pressure area formed near the target material by irradiating a beam light onto the target material is optimal, and a step for exciting and ejecting the material contained in the target material by irradiating the beam light onto the target material with introducing the ambient gas into the reaction chamber at the pressure to deposit the material on the substrate.
The present invention provides a process in which the pressure (P) of the ambient gas and the distance (D) between the substrate and the target material is controlled according to the relation PDn=constant (n is approximately 2 to 3).
According to this process, the interaction (collision, scattering, enclosing effect) between material emitted from the target upon laser irradiation (mainly atoms, ions, and clusters) and the inert gas is optimized to bring about a thin film having the self-align type crystalline structure with maintaining the stoichiometric composition.
Furthermore, the present invention provides a process in which an inert gas is used as the ambient gas. According to this process, a cold cathode is formed without introduction of oxidative gas.
Furthermore, the present invention provides a process in which the pressure of the ambient gas is in the range from 0.1 to 10 Torr. According to this process, a thin film having the same composition as that of the target material is formed suitably.
Furthermore, the present invention provides a process in which the material that constitutes the target consists of at least two or more composition.
Herein, the material that constitutes the target material is preferably any one compound of LaB6, TiC, SiC, and SnC. Otherwise, the material may be any typical nitride of TiN, BN, SrN, ZrN, and HfN, or may be any one transparent conducting material selected from a group including In2O3, SnO2, ITO, ZnO, TiO2, WO3, and CuAlO2.
Furthermore, the present invention characteristically provides an electron emission element having an electron emission part comprising a cold cathode consisting of crystalline thin film of electron emissive material formed by means of the cold cathode forming process. The above-mentioned structure is effective for realizing the reduced electron emission threshold value and the increased emission current value and stability, and for realizing the low cost with the structure simpler than the conventional structure.
Furthermore, the present invention characteristically provides an electron emission element having an electron emission part comprising a cold cathode consisting of crystalline thin film of electron emissive material formed by means of the cold cathode forming process formed on the substrate with interposition of a conductive film or resistive film. The above-mentioned structure is effective for realizing the reduced electron emission threshold value and the increased emission current value and stability, and for realizing the low cost with the structure simpler than the conventional structure.
Herein, the material that constitutes the target material is preferably any one compound of LaB6, TiC, SiC, and SnC. Otherwise, the material may be any typical nitride of TiN, BN, SrN, ZrN, and HfN.
Furthermore, the present invention characteristically provides a CRT provided with an electron emission element as the electron source. The above-mentioned structure is effective for realizing a high brightness and fine high vision CRT.
Furthermore, the present invention characteristically provides a flat display provided with an electron emission element as the electron source. The above-mentioned structure is effective to realize a low cost flat display.
Furthermore, the present invention provides an electron emission type element provided with a transparent substrate and a cold cathode comprising a crystalline thin film of electron emissive material formed on the transparent substrate.
Furthermore, the present invention provides a electron emission type element provided with a transparent substrate and a crystalline thin film of electron emissive material formed on the transparent substrate by means of the cold cathode process formed on the substrate with interposition of an interference layer consisting of conductive film or resistive film.
Herein, the crystalline thin film that constitutes the cold cathode is preferably formed of a transparent conducting material selected from a group including In2O3, SnO2, ITO, ZnO, TiO2, WO3, and CuAlO2.
Furthermore, the present invention characteristically provides a transmission type flat display provided with an electron emission element as the electron source. The above-mentioned structure brings about realization of a high brightness and fine transmission type flat display.
As described hereinabove, in a cold cathode forming process of the present invention, a target material and a substrate are provided in a reaction chamber, the pressure (P) of an ambient gas introduced into the reaction chamber and the distance (D) between the substrate and the target material are controlled so that the size of a high temperature high pressure area formed near the target material by irradiating a beam light onto the target material is optimal, and the material contained in the target material is excited and ejected by irradiating the beam light onto the target material with introducing the ambient gas into the reaction chamber at the pressure to deposit the material on the substrate. The above-mentioned structure is effective to obtain the self-align type crystalline structure easily in comparison with the conventional forming process.
According to the present invention, the electron emission part is used as the thin film electron source provided with a cold cathode having a crystalline thin film of electron emissive material formed by means of the above-mentioned cold cathode forming process. Thereby, the above-mentioned structure is effective to realize the reduced cost with the structure simpler than the conventional structure. The electron emission element having the above-mentioned structure is fabricated reproducibly, and the dispersion between elements is less, and the increased current density is realized as the multi source. Therefore, the electron emission element can be used as a high brightness and fine CRT electron source. Furthermore, a transparent substrate is used as the substrate and transparent conducting material is used as the material of the crystalline orientation film to realize a transparent flat display.
The object and advantage of the present invention will be more apparent by examples described hereinafter with reference to the drawings.